1. Field of the Invention
The present invention relates to an optical disk device, and more particularly relates to an optical disk device that is compatible with optical disks including three or more recording layers on one side.
2. Description of the Related Art
With a conventional optical disk device that is compatible with a BD (Blu-ray Disc; registered trademark)-DL (double-layer BD), adjustment of the various recording layers of the BD-DL is carried out by the following procedure upon start-up when the BD-DL is inserted into the optical disk device.
First, the optical disk is rotated, and the number of recording layers on the optical disk is acquired by performing a focus search. Next, spherical aberrations are corrected with an L0-use setting value that has been measured ahead of time in the course of manufacturing the device, etc., after which automatic gain control (automatic amplitude adjustment) of a focus error signal is performed, and focus control is performed at the recording layer L0 that is far away from the side on which the laser beam is incident. Then, rough adjustment of the spherical aberration correction is performed using a tracking error signal as an index, after which various kinds of adjustments related to the tracking error signal (such as balance adjustment, offset adjustment, and amplitude adjustment) are performed, automatic gain control of the tracking error signal is performed, and tracking control is performed. Afterward, furthermore, fine adjustment of the spherical aberration correction is performed using an RF signal as an index, and loop gain adjustment of focus control and loop gain adjustment of tracking control are carried out.
Afterward, a focus jump is made to the recording layer L1 closest to the side on which the laser beam is incident, and spherical aberrations are corrected with an L1-use setting value that has been measured ahead of time in the course of manufacturing the device, etc., after which focus control is performed on L1. Then, rough adjustment of the spherical aberration correction is performed, after which tracking control is performed. Afterward, furthermore, fine adjustment of the spherical aberration correction is performed, loop gain adjustment of focus control and loop gain adjustment of tracking control are carried out, and start-up is ended. Ending this start-up makes it possible to reproduce the BD-DL.
Thus, in the start-up operation when a BD-DL is inserted into the device, the rough adjustment of the spherical aberration correction by pulling focus control into the recording layer L0 is performed before the tracking control is placed in an ON state, that is, before address acquisition, so even if the focus control, which is supposed to be performed on the recording layer L0, is mistakenly performed on the recording layer L1, the control means of the optical disk device could not immediately detect this error.
Therefore, if focus control that is supposed to be performed on the recording layer L0 is instead mistakenly performed on the recording layer L1, in the rough adjustment of spherical aberration correction at the recording layer L0 (the focus is actually on the recording layer L1), the movable lens used for spherical aberration correction moves to the position on the recording layer L1 at which spherical aberration is roughly best, after which various kinds of adjustments are made related to the tracking error signal, and at the stage when tracking control is placed in an ON state and an address has been acquired, the control means of the optical disk device can detect that the focus control has been mistakenly performed on the recording layer L1, and an attempt is made to pull the focus control again into the recording layer L0.
Note that a limit is provided to the amount of movement of the movable lens used for spherical aberration correction in rough correction of the spherical aberration correction at the recording layer L0 in order to avoid ending up in a situation in which an error occurs in the measurement for some factor (such as stray light) when the focus control is being properly performed on the recording layer L0, and this causes the movable lens for spherical aberration correction to move so far that the tracking control cannot be placed in an ON state.
At present, as optical disks including three or more recording layers on one side, there are BDs that are compliant with a BDXL standard established in June of 2010.
For example, in the start-up operation in a case in which a BD-QL (quad-layer BD) compliant with the BDXL standard has been inserted into a device, it is possible that while focus control is supposed to be performed on the recording layer L0 that is farthest away from the side on which the laser beam is incident, the focus control will instead be mistakenly performed on a recording layer L3 that is closest to the side on which the laser beam is incident.
At the current value of the limit provided for the amount of movement of the movable lens for spherical aberration correction in rough adjustment of spherical aberration correction at the recording layer L0, when focus control that is supposed to be performed on the recording layer L0 is instead mistakenly performed on the recording layer L3, in rough adjustment of the spherical aberration correction at the recording layer L0 (the focus is actually on the recording layer L3), the movable lens for spherical aberration correction can only be moved to a position that is quite far away from the position at which the spherical aberration is roughly best at the recording layer L3. Therefore, a large deviation occurs in the various kinds of adjustments related to the tracking error signal, so there is the risk of ending up in a situation in which the tracking control cannot be placed in an ON state.
In light of this, a measure is conceivable in which the limit provided for the amount of movement of the movable lens for spherical aberration correction in rough adjustment of the spherical aberration correction at the recording layer L0 is expanded over its present value, but if this limit is expanded too much, an error may occur in the measurement for some factor (such as stray light) when the focus control is being properly performed on the recording layer L0, and this will cause the movable lens for spherical aberration correction to move so far that there is the risk of ending up in a situation in which the tracking control cannot be placed in an ON state.
Note that techniques relating to the correction of spherical aberration are disclosed in Japanese Patent Application Laid-Open Publication No. 2009-230781, Japanese Patent Publication No. 4584172, Japanese Patent Publication No. 4258542, and Japanese Patent Application Laid-Open Publication No. 2009-140573, but there is no disclosure or implication that relates to the limit provided for the amount of movement of the movable lens for spherical aberration correction in rough adjustment of spherical aberration correction at the recording layer L0 at start-up.